1. Field of the Invention
The present invention relates to a method and an apparatus for manufacturing a thin film of carbon nanotubes or the like, and a method for manufacturing an electronic device including the above thin film.
2. Description of the Related Art
Since having superior electrical and mechanical properties, carbon nanotubes (hereinafter simply referred to as “CNTs”) have been expected to be widely used in various fields as a promising material for nanotechnology, and hence fundamental research and application research of carbon nanotubes have been aggressively carried out.
Heretofore, as a method for manufacturing a CNT thin film, for example, there have been a spray method in which after a liquid containing CNTs dispersed in a solvent, such as ethanol, using ultrasonic waves is sprayed on a substrate using a spraying tool, the solvent is then evaporated to form a thin film; a Langmuir Blodgett (LB) method in which after a film made of solubilized CNTs is spread out on a water surface, operation of immersing a substrate into the water in a direction perpendicular to the surface thereof and pulling it up therefrom is repeatedly performed to form a thin film; a coating method in which a solution containing CNTs is applied to a substrate; and a filtering method in which CNTs contained in a solution is uniformly deposited on a filter and is then transferred on a substrate.
In addition, in Japanese Patent No. 3665969 (claim 1 and paragraph 0013) titled “Method for Manufacturing CNT-Containing Film and CNT-Containing Coating”, the following has been disclosed.
That is, in the method for manufacturing a CNT-containing coating film, after a first dispersion that contains at least CNTs and a solvent is applied to a surface of a substrate, the solvent of the first dispersion is removed so that CNTs form a three-dimensional net structure, and a second dispersion containing at least a resin and a solvent is applied thereto so as to infiltrate into the three-dimensional net structure of CNTs.
A film that is formed using the invention disclosed in the above Japanese Patent No. 3665969 can obtain superior conductivity and transparency even when the content of CNTs is low. In this preferable embodiment, the content of CNTs in the film is approximately 0.001 to 1 percent by weight. More preferably, the content of CNTs in the film is approximately 0.01 to 0.1 percent by weight, and as a result, superior transparency and low haze can both be obtained.
Next, in Japanese Unexamined Patent Application Publication No. 2006-298715 (paragraph 0006) titled “Manufacturing Method of CNT Thin Film, Manufacturing Method of Electronic Element, Manufacturing Method of Thin Film, Manufacturing Method of Structural Body, and Forming Method of Air Bubble”, the following has been disclosed.
That is, it was found after a CNT dispersion containing a surfactant is prepared, when air is fed thereinto to form an air bubble, and this air bubble is deposited on a substrate, a CNT thin film having significantly superior uniformity and small thickness as compared to those of a CNT film obtained by a related method can be formed with high film thickness controllability.
The reason for this is believed that CNTs present in a film which forms a surface layer of this air bubble and which is formed from the CNT dispersion are deposited on the substrate to form the CNT film.
In addition, in “High-performance electronics using dense, perfectly aligned arrays of single-walled carbon” by S. J. Kang et al, Nature Nanotechnology, 2, pp 230 to 236 (2007) (FABRICATION OF NANOTUBE ARRAYS AND DEVICES), formation of a single-wall carbon nanotube (SWCNT) array by a chemical vapor deposition (CVD) method has been disclosed.
In addition, in “Large-area blown bubble films of aligned nanowires and carbon nanotubes” by G. Yu et al, Nature Nanotechnology, 2, pp. 372 to 377 and FIG. 1 (2007), a blown-bubble films (BBFs) method has been disclosed that includes three basic steps of: (1) preparing a polymer dispersion (epoxy dispersion) of nanowires or nanotubes having a stable and controlled concentration, (2) expanding the polymer dispersion at controlled pressure and expansion rate using a circular die so as to expand an air bubble, and (3) transferring the air bubble on a substrate or an open frame structure.
In addition, an LB method for forming a CNT thin film has been disclosed in “J. AM. CHEM. SOC.” by Xiaolin Li et. al., 2007, 129, pp. 4890 to 4891; “Jpn. J. Appl. Phys.” by Yeji KIM et. al., Vol. 42 (2003), pp, 7629-7634; and “Chemistry Letters”, by Jun Matsui et. al., Vol. 35, No. 1 (2006), pp. 42 to 43.